Thermostatic switch for controlling electric circuits



Feb 24, T. CURZON THERMOSTATIC SWITCH FOR CONTROLLING ELECTRIC CIRCUITSFiled NOV. 13, 1944 l NVENTOR THoMAs CURZON IHI Patented Feb. 24, 1948THERMOSTATIC SWIT LING ELECTRI Thomas Curzon, Acton, London,

CH FOR CON TROL- C CIRCUITS England, assignor to C. A. V. Limited,London, England Application November 13, 1944, Serial No.

In Great Britain October 1, 1943 4 Claims. (Cl. 20088) This inventionrelates to thermostatic protective switches, for use in electricitydistributing systems, and has for its object to provide improvedswitches of the kind adapted to open in the event of a fault or othercondition causing an abnormal current to flow in a circuit containingthe switch, and also adapted to be prevented from automaticallyreclosing.

In the accompanying sheet of explanatory drawings,

Figure 1 is a sectional side view of a switch mechanism embodying theinvention, and Figure 2 is a diagram illustrating the electricalcnnections of the switch mechanism.

In carrying the invention into effect as shown an electromagnet d issecured in any convenient manner to a supporting plate 72 having acentral aperture, and is enclosed by a sheet metal or other casing mhaving an open end secured to the supporting plate, the other end of thecasing being closed. The electromagnet d comprises a yoke '0, awinding'e, and a spring loaded armature f, the latter having one endhingedly attached by a resilient metal strip 1) to the inner end of theyoke, and having a contact a on its other end. At a position adjacent tothe armature there is arranged within the casing m a bl-metal strip 0which at one end is secured to a metal piece q, the other end of thebi-metal strip having mounted on it a contact b adapted to co-operatewith the contact a. The ends of the electromagnet winding e areelectrically connected to the metal piece q and the electromagnet yoke 0respectively. The metal piece q is situated in part between andelectrically insulated from one side of the electromagnet yoke o and asecond metal piece 1, the latter being secured and electricallyconnected to the said yoke by screws 8 which also serve to secure thefirstmentioned metal piece in position. A third metal piece it issecured by screws u to the other side of the electromagnet yoke 0, butis electrically insulated therefrom in any convenient manner. The secondand third metal pieces r, extend through the closed end of the casing m,and are provided at their outer ends with terminal screws 1) forconnection to the circuit to be controlled.

For electrically interconnecting the first and third metal pieces q, t,I employ a push-pull switch 2' having a pair pair of complementarymovable contacts r. The fixed contacts are respectively secured to themetal pieces q, t at positions near the supporting plate a, and areformed at their adjacent sides with V-shaped recesses 31 foraccommodating of fixed contacts w and aiiti complementary parts of themovable contacts r. The latter are interconnected by a resilient metalbridge piece 2, and are operable by an axially movable stem 2 whichpasses through the central aperture in the supporting plate n and isprovided at its outer end with a finger piece 3 made from insulatingmaterial. The finger piece 3 is formed with a tubular extension 4 whichis slidable in a fixed tubular guide 5 on the supporting plate n. Thestem 2 passes through a central hole in the bridge piece 2 and issurrounded by a pair of helical compression springs 6 through whichmovement can be imparted by the stem to the bridge piece for actuatingthe movable contacts 3:, one of the springs being situated between thebridge piece and the finger piece 3, and the other being situatedbetween the bridge piece and a head 1 on the inner end of the stem.Secured to the supporting plate 11 and situated between the latter andthe fixed contacts w are a pair of insulating pieces 8 which at theiradjacent sides are also formed with V-shaped recesses 9 foraccommodating the movable contacts :r.

- The contacts a, b, are normally closed, and when in this conditionthey short-circuit the electromagnet winding e which is of relativelyhigh resistance. Assuming that the main switch 1' is closed and that themetal pieces r, t, are connected to the circuit to be controlled, thecon tacts a, b remain closed so long as normal conditions exist in thesaid circuit, but in the event of a short-circuit or other conditioncausing abnormal heating of the strip 0 the said contacts are separated,whereupon current flows through the Winding e and excites theelectromagnet d. This causes rapid and complete separation of thecontacts a, b and prevents reclosure thereof in consequence of the strip0 cooling, When removing the fault the main switch 2 is opened. Theelectromagnet d then ceases to act, and the cooled strip 0 allows thecontacts a, b, to come together again.

When the switch 2' is closed its movable contacts a: engage the recesses11 in the fixed contacts 20. To open this switch a pull is exerted onthe finger piece 3. The effect of this is to compress the spring 6arranged between the bridgepiece z and the head 1 of the stem 2 untilthis spring causes the movable contacts a: to be disengaged from therecesses 11 in the fixed contacts w and moved into engagement with therecesses 9 in the insulating pieces 8. Reclosure of the switch 2 iseffected by exerting a push on the finger piece 3. This causes the otherspring 8 to be compressed until it causes the movable contacts a: to bedisengaged from the recesses 9 and re-engaged with the recesses 11. Itwill be seen therefore that both the opening and closing movements ofthe contacts a: are effected rapidly under spring action.

If desired the position of the contact b may be adjusted by a set screwl carried by the metal piece q and acting on the bi-metal strip 0.

Whilst I prefer to employ bi-metal strip for the separation of thenormally closed contacts on account of its simplicity and convenience, Imay in some cases employ any other convenient thermally deformable meansfor separating the contacts.

Having thus described my invention what I claim as new and desire tosecure by Letters Patent is:

. 1. A thermostatic switch of the kind specified, having in combinationa pair of normally closed and independently movable contacts, a heatresponsive device, and an electromagnet having its winding permanentlyconnected across said contacts, one of said contacts being movable bysaid heat responsive device to cause separation of said contacts and theother contact bein arranged to be attracted and actuated by saidelectromagnet, so that in the event of separation of said contacts bysaid heat responsive device said contacts are held apart by saidelectromagnet.-

2. A thermostatic switch as claimed in claim 1, in which the normallyclosed and independently movable contacts are respectively carried by abi-metal strip forming the heat responsive device and by an armatureforming a part of the electromagnet.

3. A thermostatic switch as claimed in claim 1 and having in an electriccircuit containing the normally closed and independently movable con=tacts, a controlling push-pull switch, the two switches being formed asa unitary structure.

4. A thermostatic switch as claimed in claim 1 and having in an electriccircuit containing the normally closed and independently movable contacts, a controlling push-pull switch comprising in combination a pairof fixed contacts, a pair of resiliently interconnected movable contactsadapted to co-operate with said fixed contacts, an operating member andsprings through which movement can be imparted to said resilientlyinterconnected movable contacts under the action of said operatingmember, the two switches being formed as a unitary structure.

THOMAS CURZON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 29,015 Siemens Bros. -19041,336,418 Broeger Apr. 13, 1920 1,561,240 Johnston Nov. 10, 19251,564,938 Chandeysson Dec. 8, 1925 1,763,649 Goetz June 17, 19302,087,216 Betz July 13, 1937 2,313,969 Riche Mar. 16, 1943 2,338,731Morse Jan. 11, 1944 FOREIGN PATENTS Number Country Date 471,946 Germany1929

